Trailing-edge jets for UCAV's flight control over a wide speed range

Abstract

With fluidic control effectors, the flying-wing aircraft have been expected to achieve flapless fight which can reduce the radar cross section (RCS). However, most researches are focused on their control capability at low speed (Ma<0.3). This paper numerically investigates using trailing-edge jets (TE jets) to control a flying-wing UCAV over a wide speed range (Ma=0.145∼0.7) to evaluate 3-axis flight control capability, bleeding air impacts on engine performance, and stealth improvement. The three-dimensional flow is simulated by a Reynolds–averaged Navier–Stokes (RANS) solver with k−ω SST turbulence model. The power consumption of bleeding air is converted into additional drag, and the control efficiency factor is proposed to compare the efficiency of fluidic and solid control effectors under a unified framework. The RCS is evaluated by the Large Element Physical Optics (LEPO) solver. The results show that, for pitch and roll control, TE jets relying on circulation control (CC) can produce the same moment as control surfaces deflected 30°, 20°, and 10° at Ma=0.145,0.4, and 0.7, respectively. Meanwhile, TE jets have less effect on the engine mass flow and thrust, and are more efficient at producing control moments than control surfaces. For yaw control, relying on the recoil effect, TE jets' control capability is equal to that of split flaps at low speed with relatively higher bleeding air impacts on engine performance, but will not be affected by the flow separation at the high angle of attack. For stealth characteristics, the RCS of jet-controlled UCAV in frontal, lateral, and some specific azimuth ranges reduces remarkably. This study indicates that TE jets are highly promising pitch and roll control effectors for a flying-wing UCAV to enhance survivability from low speed to high subsonic speed.